1. Field of the Invention
This invention relates to a technique for facilitating replacement/repair of a laser output element in an optical head device for carrying out recording/reproducing by irradiating an optical disk with a laser beam.
2. Description of the Related Art
For example, in an optical head device for carrying out recording/reproducing for a CD (compact disk), DVD (digital versatile disk), an optical-disk for a blue-violet laser, etc., a configuration is known in which a frame (hereinafter referred to as a sub-frame) to which a semiconductor laser is attached is provided as a body separated from a base frame to which various optical systems for guiding a laser beam to the optical disk are attached, and the sub-frame is moved to carry out position alignment of the semiconductor laser when said sub-frame is secured to the base frame.
More specifically, the position alignment is carried out in such a manner that while the strength of the laser beam produced from the semiconductor laser is measured through an optical system of the base frame, the sub-frame to which the semiconductor laser is fixed is moved along a mating face of the base frame in X and Y directions vertical to an optical axis. The position with the highest detected strength of the laser beam is found as an optimum position, and the sub-frame is secured to the base frame at that position using e.g. screw.
Conventionally, it is general that the base frame is formed of e.g. zinc die-cast, and the sub-frame to which the semiconductor laser is attached is formed of e.g. aluminum so that it can serve as a heatsink plate for the semiconductor laser.
JP-A-3-165321 discloses a component assembled structure which is a technique preferably applied to the place where the optical head is attached to an electronic base plate.
In order to record data on the optical disk, a large laser output is required. In addition, in order to carry out the recording at a high speed, the required laser output also must increase. On the other hand, the semiconductor laser has a feature that it is likely to generate deterioration in a high output region.
Thus, as the head device in which write is carried out at the high speed prevails from now on, it is expected that in many cases, the replacement/repair of the semiconductor laser due to its deterioration is required.
However, as regards a conventional fixed structure of the semiconductor laser, it has been found that when replacement of the semiconductor laser is carried out, the following inconvenience occurs in many cases. Specifically, in the above fixed structure, since the base frame and sub-frame to which the semiconductor laser is attached are formed of a relatively soft metal such as zinc die-cast and aluminum, for example, at the time of the first alignment of the semiconductor laser or screwing of the sub-frame, deformation of a flaw or groove called “galling” may occur on the mating surfaces.
If the galling is generated, when the laser output element is replaced together with the sub-frame by a new element, the following inconvenience occurs. Namely, when the sub-frame is slid for position alignment of the semiconductor laser, the galling” generated on the mating surfaces hinders the sub-frame from being moved smoothly.
Such a problem may also occur in assembling a new product. Specifically, as a result of the decision that the semiconductor laser itself or its fixed position is defective after the sub-frame has been secured, where the semiconductor laser is replaced together with the sub-frame or the sub-frame is fixed again, the galling generated on the mating surfaces hinders such an operation as described above. Thus, the base frame and the step of attaching an optical system thereto are useless, which reduces the yield of the products.
It has been examined to apply the technique disclosed in JP-A-3-165321 to the place where the sub-frame with the semiconductor laser and the base frame are secured to each other. When a film member of fluororesin is inserted in between the mating faces of the sub-frame and the base frame, no galling is generated in the sub-frame and the base frame. However, since the film member is made of the resin, this film member is easily deformed owing to tightening of the sub-frame, thereby giving rise to various problems. For example, when the sub-frame is tightened strongly, the film member will be crushed to be damaged. Inversely, when the sub-frame is tightened weakly, the fixing position may be displaced over a long time of period owing to the elasticity generated by the deformation of the film member.
Further, JP-A-3-165321 also discloses a method of coating the mating surfaces with resin such as fluororesin. However, where a metal is coated with the fluororesin, the coated film is very likely to be peeled off. The base frame and sub-frame coated in this way cannot be adopted.